Powerfeed polymers having improved block resistance performance

Abstract

The present invention provides emulsion copolymers and coating compositions containing the same having improved room temperature and hot block resistance in coatings wherein the copolymers have a broad measured glass transition temperature and are the copolymerization product of a vinyl monomer composition A and a softer vinyl monomer composition B having a Hansch parameter of at least 3.2, and containing one or more vinyl monomer M, such that each of which vinyl monomer(s) M would when homopolymerized provide a homopolymer having a measured Tg of 20° C. or less, such as, for example, 2-ethylhexyl acrylate. In addition, the present invention provides methods for making the emulsion copolymers by a powerfeed process comprising feeding vinyl monomer composition A into a reactor from a feed vessel while feeding, simultaneously or after a delay, vinyl monomer composition B into the feed vessel while polymerizing the monomers in the reactor.

We claim: 
     
       1. A composition comprising one or more emulsion copolymer which has a broad measured glass transition temperature (measured Tg) and which are the copolymerization product residue of from 20 to 80 wt. %, based on the total weight of monomers used to make the copolymer, of vinyl monomer composition A containing one or more vinyl monomer A, and from 20 to 80 wt. %, based on the total weight of monomers used to make the copolymer, of vinyl monomer composition B having a Hansch parameter of at least 3.2, and containing one or more vinyl monomer M, such that each of which vinyl monomer(s) M would when homopolymerized provide a homopolymer having a measured Tg of 20° C. or less, wherein the total amount of vinyl monomer(s) M in vinyl monomer composition B is from 30 to 100 wt. % of the total amount vinyl monomer(s) M used in vinyl monomer compositions A and B, and, further wherein, the vinyl monomer compositions A and B are selected such that a single-stage copolymer made from the total vinyl monomer composition used to make the emulsion copolymer would have a measured Tg of from 0 to 70° C. 
     
     
       2. The composition as claimed in  claim 1 , wherein the vinyl monomer composition A, has a measured Tg of 0° C. or more. 
     
     
       3. The composition as claimed in  claim 1 , wherein vinyl monomer M would when homopolymerized provide a homopolymer having a measured Tg of 0° C. or less. 
     
     
       4. The composition as claimed in  claim 1 , wherein vinyl monomer M is chosen from 2-ethylhexyl acrylate, 2-propylheptyl acrylate, and lauryl acrylate. 
     
     
       5. The composition as claimed in  claim 1 , the vinyl monomer compositions A and B are selected such that a single-stage copolymer made from the total vinyl monomer composition used to make the emulsion copolymer would have a measured Tg of from 3° C. to 20° C. 
     
     
       6. The composition as claimed in  claim 1 , wherein vinyl monomer composition A or vinyl composition B is acrylic or styrene acrylic. 
     
     
       7. A method for making the emulsion copolymer of  claim 1  comprising providing separately vinyl monomer composition A in a primary feed vessel, and vinyl monomer composition B, including vinyl monomer M in a secondary feed vessel, continuously introducing the contents of the primary feed vessel into a polymerization vessel and continuously feeding vinyl monomer composition B into the primary feed vessel while emulsion polymerizing the monomers in the polymerization vessel until vinyl monomer compositions A and B are polymerized. 
     
     
       8. The composition as claimed in  claim 1 , which is a coating composition containing the emulsion copolymer and has a volatile organics content (VOC) of 155 g/l or less. 
     
     
       9. The composition as claimed in  claim 8 , wherein the VOC content is 105 g/l or less. 
     
     
       10. The composition as claimed in  claim 1 , further comprising benzophenone.